Cell specialization

The process by which an **unspecialized cell** develops into a **specialized cell** with a particular structure and function.

A cell that has **no particular job yet** and can still develop into different cell types (e.g. a stem cell).

A cell with a **particular structure suited to one particular function** (e.g. a neuron or red blood cell).

**Differentiation**.

**Differentiation** — it produces the specialized cell types that group into tissues.

**Cell division (mitosis)** makes **more** cells (identical copies); **differentiation** makes cells **different** (specialized).

**Cell division (mitosis)** — it makes more identical cells.

**Differentiation** — it makes cells become different from one another.

First **cell division** makes many identical cells, then **differentiation** makes them into specialized types.

So cells can **specialize for one job each** (division of labour), letting the whole organism do many jobs efficiently.

From **'different'** — it makes cells become **different from one another** (specialized).

**Yes** — they all came from the same original cell and share the same genes, but they differentiated into different types.

The process by which an **unspecialized cell becomes a specialized cell** with a particular structure and function.

**Yes** — every body cell carries the same complete set of genes (the same genome).

**Different genes are expressed** (switched on) in each cell type — not different genes present.

Switching a gene **'on'** so it is used to make its **protein**. An expressed gene is active; an unexpressed gene is silent.

Expressing **only some** of the genes in the genome — different genes in different cell types — so each cell makes only the proteins it needs.

**Chemical signal gradients** — the concentration of signalling molecule a cell meets depends on its **position**.

A smooth change in the concentration of a signalling molecule — **high near its source**, lower further away.

A cell's **position** sets the **signal concentration** it meets, which switches on a **particular set of genes**, deciding the cell type it becomes.

It **differentiates** — switching on specific genes and becoming a specialized cell type.

The genes switched on are used to make **specific proteins**, which give the cell its specialized **structure and function**.

**No** — unused genes are switched **off**, not removed. The cell keeps the full genome.

Position in gradient → **signal concentration** detected → **genes** switched on → **proteins** made → specialized **cell type**.

An **unspecialized** cell that can **self-renew** (keep dividing) and **differentiate** into specialized cell types.

**Self-renewal** (divides to make more stem cells) and **differentiation** (becomes specialized cells). Both are needed.

A measure of **how many different cell types** a stem cell can differentiate into.

Can become **any cell type plus the placenta**. Example: the **zygote** / very early embryo.

Can become **any cell type of the body** (but not the placenta). Example: **embryonic stem cells**.

Can become a **limited family of related** cell types. Example: **blood-forming cells in red bone marrow**.

Can become **only one** cell type.

**Totipotent** cells can also form the **placenta**; **pluripotent** cells cannot.

Potency **decreases** (and specialization increases) as cells differentiate — adult stem cells are usually only multipotent or unipotent.

The **location in the body** where a particular stem cell is found (e.g. red bone marrow for blood-forming stem cells).

**Multipotent** (forms the family of blood cells); niche = the **red bone marrow**.

In the **early embryo** — they are the **embryonic stem cells**.

An **unspecialized** cell that can **divide (self-renew)** and **differentiate** into one or more specialized cell types.

They can **divide** to make many cells, and they can **differentiate** into the specialized cell type that is needed.

A stem cell's ability to **divide by mitosis** to make more cells (including more stem cells), so the supply is not used up.

The process by which an **unspecialized** cell becomes a **specialized** cell with a particular structure and function.

They **divide** to make many new cells, then **differentiate** into the exact lost cell type, replacing the missing cells and restoring function.

Because they can **divide** to make enough cells and **differentiate** into the specific specialized cell that was lost.

From **very early embryos**; they can become **almost any** cell type (very flexible).

From **body tissues** such as **bone marrow**; they can become only a **few** related cell types.

They are taken from an **early embryo**, which would otherwise develop — this raises **ethical objections**.

**No embryo is used** — they are taken from body tissues, often from the patient themselves.

**Replacing cells lost to disease or injury** (e.g. blood, nerve or skin cells) that the body cannot regrow on its own.

A **rise in cell number** shows **division**; the appearance of **named specialized cells** shows **differentiation**.

A cell whose **structure is adapted** to carry out a **particular function** efficiently.

By **differentiation** — switching on (expressing) a particular set of their genes.

**Structure follows function** — a cell's shape and contents match the job it does.

**Biconcave** shape (large surface area) and **no nucleus** → more room for **haemoglobin** to carry O₂.

**Microvilli** give a large **surface area**; **many mitochondria** supply **energy (ATP)** for active transport.

A **tail (flagellum)** and many **mitochondria** → energy to **swim** to the egg.

A very **long fibre (axon)** → carries **electrical impulses** over long distances.

**Column shape near the upper leaf surface**, packed with **chloroplasts** → absorbs the most **light**.

A **long, thin projection** into the soil → large **surface area** to absorb **water and minerals**.

The **egg cell (ovum)** — it stores **food reserves** for the early embryo.

The **sperm cell** (stripped down to swim) and the **red blood cell** (small and flexible for capillaries).

In **feature → function pairs** — name a structure AND the job it makes possible; one mark per linked pair.

A cell that fits the standard description: **one nucleus**, **microscopic** size, and its **own sealed membrane** (and wall in plants/fungi).

A cell that **does not fit the typical description** — e.g. it lacks a nucleus, has many nuclei, is unusually large, or shares its cytoplasm.

Having **no nucleus**. ('a-' = without.)

Having **many nuclei** inside one cell or fibre. ('multi-' = many.)

Having **no cross-walls (septa)**, so the cytoplasm is **continuous** — seen in some fungal hyphae.

A **mature mammalian red blood cell** and a **phloem sieve tube element** — both lose their nucleus.

A **skeletal (striated) muscle fibre** — many cells **fuse** into one long fibre with many nuclei.

To leave **more room for haemoglobin**, so it can **carry more oxygen**.

It breaks the rule that cells are microscopic — a **single cell** can be **several centimetres long**.

It has **no cross-walls**, so the **cytoplasm is continuous** and **many nuclei are shared** along the thread.

**Adaptations** — each unusual feature usually helps the cell do a **specific job**.

**Zero** nuclei = anucleate; **many** nuclei = multinucleate; **one** nucleus = typical.